Type 339 Programmed Buffered Display

This document is a comprehensive technical manual for the Type 339 Programmed Buffered Display System, an on-line interactive graphics system developed by Digital Equipment Corporation. It describes the hardware, interface, operation, and programming of the display, which connects to a PDP-9 computer.

The system comprises a precision incremental CRT display, control logic, a light pen, a pushbutton control box, and interface logic. Functioning as a dual-processor system, the display and PDP-9 share computer memory, with the display processor utilizing a Direct Memory Access (DMA) channel for high-speed data transfer and the I/O bus for commands.

The document details seven core display modes: Point, Increment, Vector, Vector-Continue, Short Vector, Graph-Plot, and Character Mode (supported by optional hardware or software character generators). It outlines various options, including different character generators (VC38, VA38), a slave option (VS38) for connecting up to eight CRTs, a search option (VF38) for display file analysis, a zoom option (VZ38), track balls, and graphic tablets.

Interface considerations are thoroughly covered, explaining the Program Interrupt Facility, Automatic Priority Interrupt Option, DMA Channel, and I/O Skip Facility for communication between the display and PDP-9. This includes the VL09 interface logic's role in signal conversion and interconnection.

A significant portion of the manual is dedicated to the display system's internal registers, such as the Display Address Counter (DAC), Delta-X and Delta-Y Registers, Pushdown Pointer (PDP) for subroutining, Mode Register, Intensity and Scale Registers, and X/Y Position Registers, along with character generator specific registers. It differentiates between control-state instructions (for setting parameters, jumps, and skips) and data-state instructions (for controlling CRT beam movement).

Operational and programming information is extensively provided, including descriptions of system controls, light pen usage, and how to program the display using Input/Output Transfer (IOT) instructions. It explains display parameters like coordinate systems, scaling, and intensity levels, as well as the behavior of various display flags (e.g., Internal Stop, External Stop, Edge, Light Pen, Pushbutton Hit, Manual Interrupt) which can trigger computer interrupts. Timing specifications for different operations are also detailed.

The document concludes with appendices offering diagnostic programs, programming examples illustrating display operations, and comprehensive reference tables summarizing all control-state and data-state commands, mnemonics, IOT instructions, and status formats.